Process for producing cation exchangers

ABSTRACT

Strongly acidic cation exchangers with high mechanical, osmotic and oxidation stability can be prepared by sulfonating bead polymers formed from one or more vinylaromatic monomer(s), one or more crosslinker(s) and from 0.2 to 20% by weight of one or more vinyl ethers and/or vinyl esters.

The invention relates to a process for producing strongly acidic cationexchangers with high mechanical, osmotic and oxidation stability bysulfonating bead polymers formed from one or more vinylaromaticmonomer(s), one or more crosslinker(s) and one or more ether(s) and/orester(s) of vinyl alcohol.

BACKGROUND OF THE INVENTION

Strongly acidic cation exchangers can be obtained by functionalizingcrosslinked styrene bead polymers. The functionalization generatescovalently bonded sulfonic acid groups through reaction of aromaticunits of the polymer skeleton with a sulfonating agent, for examplesulfuric acid.

One problem with the known strongly acidic cation exchangers is that oftheir stability under stress, which is not always sufficient. Forinstance, cation exchanger beads can break up as a result of mechanicalor osmotic forces. For all applications of cation exchangers, theexchangers present in bead form must maintain their habit and must notbe degraded partly or even entirely during the application or break upinto fragments. Fragments and bead polymer splinters can get into thesolutions to be purified during the purification and contaminate themthemselves. Moreover, the presence of damaged bead polymers isunfavorable for the functioning of the cation exchangers themselveswhich are used in column processes. Splinters lead to an elevatedpressure drop of the column system and hence reduce the throughput ofthe liquid to be purified through the column.

A further problem of the known strongly acidic cation exchangers istheir tendency to release sulfonated, water-soluble fragments from waterin use as a result of the action of a wide variety of differentoxidizing agents dissolved in water (atmospheric oxygen, hydrogenperoxide, vanadyl salts, chromates). This phenomenon, known in generalto those skilled in the art by the term “leaching” leads to theenrichment of sulfonated organic constituents in the water to betreated, which can lead to various problems in the downstream systemswhich are reliant on the supply of fully demineralized water. Forexample, the water-soluble fragments lead, for example, to corrosionproblems in the cooling circuit of power plants, to defects in themicrochips produced in the electronics industry, to the failure of thesystem owing to excessively high electrical conductivity of the water ineroding machines.

There has been no lack of attempts to provide strongly acidic cationexchangers which have an improved mechanical stability, osmoticstability and/or an improved oxidation stability.

For instance, the mechanical and osmotic stability of strongly acidiccation exchangers can be increased via two-stage structure of the beadpolymers, in a so-called seed-feed process. Such processes aredescribed, for example, in EP 0 101 943 A2, EP-A 1 000 659 and DE-A 10122 896. The cation exchangers produced in two stages exhibit anoutstanding mechanical stability, but release significantly moresulfonated degradation products to the treated water than the resinsproduced in one stage.

The incorporation of small amounts of acrylate monomers into thestyrene-divinylbenzene copolymer also leads to an increased mechanicalstability, as described in U.S. Pat. No. 4,500,652 and DE-A 3 230 559.However, the presence of acrylic acid units in the polymer structureleads to a higher oxidation susceptibility of the resins.

Bachmann et al. describe in EP-A 868 444, a process for producingmechanically and osmotically stable cation exchangers by sulfonatingwithout addition of chlorinated swelling agents at temperatures between125 and 180° C. However, dispensing with the chlorinated swelling agentin the sulfonation does not improve the oxidation stability of theresins.

The oxidation stability of the strongly acidic cation exchangers can beincreased by adding antioxidants, as described, for example, in EP-A 0366 258. These antioxidants are washed slowly out of the resin, whichleads to the release of organic constituents to the water treated.Furthermore, they are spent after a relatively short time in use.Thereafter, the resin treated with antioxidants exhibits the sameoxidation sensitivity as a conventional strongly acidic cationexchanger.

The oxidation stability of the strongly acidic cation exchangers canalso be improved by increasing the crosslinking density of the beadpolymer. However, the incorporation of major amounts of crosslinkermakes the polymers more brittle, which leads to a significant reductionin the mechanical stability of the beads. Moreover, the kinetics of thecation exchange decrease significantly with increasing crosslinkingdensity, which leads to insufficient absorption capacities in manyapplications.

There is thus still a need for cation exchangers with rapid exchangekinetics, high mechanical and osmotic stability, and simultaneously highoxidation stability.

The problem addressed by the present invention is therefore that ofproviding a simple, robust and economically viable process for producingcation exchangers with rapid exchange kinetics, high mechanical andosmotic stability, and high oxidation stability.

SUMMARY OF THE INVENTION

The solution to the problem and hence the subject-matter of the presentinvention is a process for producing strongly acidic cation exchangersby sulfonating crosslinked bead polymers formed from vinylaromaticmonomers, wherein the bead polymers comprise from 0.2 to 20% by weightof vinyl ethers and/or vinyl esters as comonomer(s).

Surprisingly, cation exchangers which are obtained by the processaccording to the invention have a significantly higher oxidationstability as compared with the prior art, coupled with equal or highermechanical and osmotic stability. It has additionally been found that,surprisingly, the improvement in the oxidation stability of the stronglyacidic cation exchangers obtained from the inventive bead polymers isattributable solely to the incorporation of the comonomer in the beadpolymer, irrespective of in what manner and at what time the comonomeris added and polymerized in the course of formation of the bead polymer.

For clarification, it should be noted that the scope of the inventionencompasses all definitions and parameters cited below, in general orwithin areas of preference, in all combinations.

Crosslinked bead polymers suitable in accordance with the invention arecopolymers of at least one monoethylenically unsaturated aromaticmonomer, at least one crosslinker and at least one vinyl ether or vinylester.

The monoethylenically unsaturated aromatic (=vinylaromatic) monomersused are preferably styrene, α-methylstyrene, vinyltoluene,ethylstyrene, t-butylstyrene, chlorostyrene, bromostyrene,chloromethylstyrene or vinylnaphthalene. Also very suitable are mixturesof these monomers. Particular preference is given to styrene andvinyltoluene.

Crosslinkers are added to the monomers. Crosslinkers are generallypolyethylenically unsaturated compounds, preferably divinylbenzene,divinyltoluene, trivinylbenzene, octadiene or triallyl cyanurate. Thevinylaromatic crosslinkers are more preferably divinylbenzene andtrivinylbenzene. Very particular preference is given to divinylbenzene.To prepare the bead polymers, it is possible to use technical-gradequalities of divinylbenzene which, as well as the isomers ofdivinylbenzene, comprise customary by-products such asethylvinylbenzene. According to the invention, technical-grade qualitieswith divinylbenzene contents of from 55 to 85% by weight areparticularly suitable.

The crosslinkers can be used alone or as a mixture of differentcrosslinkers. The total amount of crosslinkers for use is generally from0.1 to 80% by weight, preferably from 0.5 to 60% by weight, morepreferably from 1 to 40% by weight, based on the sum of theethylenically unsaturated compounds.

The comonomer(s) used are vinyl ethers and/or vinyl esters.

In the context of the present invention, vinyl ethers are understood tomean the ethers of vinyl alcohol and of isopropenyl alcohol. Vinylethers in the context of the present invention may contain one or morevinyl or isopropenyl alcohol units. Preference is given to alkyl andhydroxyalkyl ethers having from 1 to 18 carbon atoms, and ethers withcondensation products of ethylene glycol. Particular preference is givento methyl vinyl ether, ethyl vinyl ether, ethylene glycol monovinylether, ethylene glycol divinyl ether, diethylene glycol monovinyl ether,diethylene glycol divinyl ether, butanediol monovinyl ether, butanedioldivinyl ether, methyl isopropenyl ether or ethyl isopropenyl ether. Veryparticular preference is given to using ethylene glycol divinyl ether,diethylene glycol divinyl ether and butanediol divinyl ether.

In the context of the present invention, vinyl esters are understood tomean the esters of vinyl alcohol and of isopropenyl alcohol. Vinylesters in the context of the present invention may contain one or morevinyl or isopropenyl alcohol units. Preference is given to esters ofcarboxylic acids having from 1 to 18 carbon atoms. Particular preferenceis given to using vinyl formate, vinyl acetate, vinyl propionate, vinylbutyrate, vinyl valerate, vinyl hexanoate, vinyl octoate, vinyldecanoate, vinyl laurate, vinyl myristate, vinyl oleate, vinylpalmitate, vinyl benzoate, divinyl phthalate or isopropenyl acetate.Very particular preference is given to using vinyl acetate andisopropenyl acetate.

It is also possible to use mixtures of vinyl ethers, mixtures of vinylesters or mixtures of vinyl ethers with vinyl esters.

The comonomer is used in amounts of from 0.2 to 20% by weight, based onthe sum of vinylaromatic monomers and crosslinkers. Preference is givento using amounts of from 0.5 to 15% by weight, more preferably from 1 to10% by weight. When mixtures of vinyl ethers and/or vinyl esters areused, the amounts are based on the sum of all comonomers.

In a preferred embodiment of the present invention, the comonomer can beadded to the monomer mixture before the polymerization sets in. However,it can also be metered in in the course of the polymerization,preferably at a polymerization conversion between 10 and 90%, morepreferably between 15 and 80%.

In a further preferred embodiment of the present invention, thecomonomer is added to the aqueous phase in the course of thepolymerization together with a water-soluble initiator. Suitablewater-soluble initiators in this preferred embodiment are compoundswhich form free radicals when the temperature is increased. Preferenceis given to peroxodisulfates, particular preference to potassiumperoxodisulfate, sodium peroxodisulfate and ammonium peroxodisulfate,water-soluble azo compounds, more preferably2,2′-azobis(2-amidinopropane)hydrochloride,2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]tetrahydrate,2,2′-azobis[N,N′-dimethyleneisobutyramidine], 4,4′-azobis(4-cyanovalericacid), and also hydroperoxides, more preferably t-butyl hydroperoxideand cumyl hydroperoxide.

However, the comonomer can also be added after the polymerization of thebead polymer has ended and can be polymerized in a separatepolymerization step.

In a preferred embodiment of the present invention, it is also possibleto add pore formers, known as porogens, to the monomers. The porogensserve for the formation of a pore structure in the nonfunctional beadpolymer. The porogens used are preferably organic diluents. Particularpreference is given to using those organic diluents which dissolve inwater to an extent of less than 10% by weight, preferably less than 1%by weight. Especially suitable porogens are toluene, ethylbenzene,xylene, cyclohexane, octane, isooctane, decane, dodecane, isododecane,methyl isobutyl ketone, ethyl acetate, butyl acetate, dibutyl phthalate,n-butanol, 4-methyl-2-pentanol or n-octanol. Very particular preferenceis given to toluene, cyclohexane, isooctane, isododecane,4-methyl-2-pentanol or methyl isobutyl ketone. The porogens used mayalso be uncrosslinked, linear or branched polymers, for examplepolystyrene and polymethyl methacrylate. Also suitable are mixtures ofdifferent porogens.

The porogen is used typically in amounts of from 10 to 70% by weight,preferably from 25 to 65% by weight, based in each case on the sum ofthe ethylenically unsaturated compounds.

To prepare the crosslinked bead polymers, the abovementioned monomers,in a further preferred embodiment of the present invention, arepolymerized in the presence of a dispersing assistant using an initiatorin aqueous suspension.

The dispersing assistants used are preferably natural and syntheticwater-soluble polymers. Particular preference is given to using gelatin,starch, cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone,polyacrylic acid, polymethacrylic acid or copolymers of (meth)acrylicacid and (meth)acrylic esters. Very particular preference is given tousing gelatins or cellulose derivatives, especially cellulose esters andcellulose ethers, such as carboxymethylcellulose, methylcellulose,hydroxyethylcellulose or methylhydroxyethylcellulose. The amount of thedispersing assistants used is generally from 0.05 to 1%, preferably from0.1 to 0.5%, based on the water phase.

In a further preferred embodiment of the present invention, initiatorsare used in the monomer mixture. In the present invention, the monomermixture refers to the mixture of vinylaromatic monomers, crosslinker(s),comonomer(s) and if appropriate porogen(s). Suitable initiators arecompounds which form free radicals when the temperature is increased anddissolve in the monomer mixture. Preference is given to peroxycompounds, particular preference to dibenzoyl peroxide, dilaurylperoxide, bis(p-chlorobenzoyl) peroxide, dicyclohexyl peroxydicarbonateor tert-amylperoxy-2-ethylhexane, and also to azo compounds, particularpreference to 2,2′-azobis(isobutyronitrile) or2,2′-azobis(2-methylisobutytonitrile), or else aliphatic peroxy esters,preferably tert-butyl peroxyacetate, tert-butyl peroxyisobutyrate,tert-butyl peroxypivalate, tert-butyl peroxyoctoate, tert-butylperoxy-2-ethylhexanoate, tert-butyl peroxyneodecanoate, tert-amylperoxypivalate, tert-amyl peroxyoctoate, tert-amylperoxy-2-ethylhexanoate, tert-amyl peroxyneodecanoate,2,5-bis(2-ethylhexanoylperoxy)-2,5-dimethylhexane,2,5-dipivaloyl-2,5-dimethylhexane,2,5-bis(2-neodecanoylperoxy)-2,5-dimethylhexane, di-tert-butylperoxyazelate or di-tert-amyl peroxyazelate.

The initiators which are soluble in the monomer mixture are employedgenerally in amounts of from 0.05 to 6.0% by weight, preferably from 0.1to 5.0% by weight, more preferably from 0.2 to 2% by weight, based onthe sum of the ethylenically unsaturated compounds.

The water phase may comprise a buffer system which adjusts the pH of thewater phase to a value between 12 and 3, preferably between 10 and 4.Particularly suitable buffer systems contain phosphate, acetate, citrateor borate salts.

It may be advantageous to use an inhibitor dissolved in the aqueousphase. Useful inhibitors include both inorganic and organic substances.Examples of inorganic inhibitors are nitrogen compounds such ashydroxylamine, hydrazine, sodium nitrite or potassium nitrite. Examplesof organic inhibitors are phenolic compounds such as hydroquinone,hydroquinone monomethyl ether, resorcinol, pyrocatechol,tert-butylpyrocatechol, condensation products of phenols with aldehydes.Further organic inhibitors are nitrogen-containing compounds, forexample diethylhydroxylamine and isopropylhydroxylamine. Resorcinol ispreferred as an inhibitor. The concentration of the inhibitor is 5-1000ppm, preferably 10-500 ppm, more preferably 20-250 ppm, based on theaqueous phase.

The organic phase can be dispersed into the aqueous phase as droplets bystirring or by jetting. The organic phase is understood to mean themixture of monomer(s) and crosslinker(s), and also, if appropriate,additionally porogen(s) and/or initiator(s). In conventional dispersionpolymerization, the organic droplets are generated by stirring. On the 4liter scale, stirrer speeds of from 250 to 400 rpm are typically used.When the droplets are generated by jetting, it is advisable to maintainthe homogeneous droplet diameter by encapsulating the organic droplets.Processes for microencapsulating jetted organic droplets are described,for example, in EP 0 046 535, whose contents in relation tomicroencapsulation are encompassed by the present application.

The mean particle size of the unencapsulated or encapsulated monomerdroplets is 10-1000 μm, preferably 100-1000 μm.

The ratio of the organic phase to the aqueous phase is generally from1:20 to 1:0.6, preferably from 1:10 to 1:1, more preferably from 1:5 to1:1.2.

However, the organic phase can also, according to EP-A 0 617 714 whoseteaching is encompassed by the present application, be added in theso-called seed-feed process to a suspension of seed polymers whichabsorb the organic phase. The mean particle size of the seed polymersswollen with the organic phase is 5-1200 μm, preferably 20-1000 μm. Theratio of the sum of organic phase +seed polymer relative to the aqueousphase is generally 1:20 to 1:0.6, preferably 1:10 to 1:1, morepreferably 1:5 to 1:1.2.

The polymerization of the monomers and comonomers is performed atelevated temperature. The polymerization temperature is guided by thedecomposition temperature of the initiator and is typically in the rangefrom 50 to 150° C., preferably from 60 to 130° C. The polymerizationtime is from 30 minutes to 24 hours, preferably from 2 to 15 hours.

At the end of the polymerization, the crosslinked bead polymers areremoved from the aqueous phase, preferably on a suction filter, andoptionally dried.

The crosslinked bead polymers are converted to cation exchangers bysulfonation. Useful sulfonating agents include sulfuric acid,chlorosulfonic acid and sulfur trioxide. Preference is given to usingsulfuric acid.

The sulfuric acid is used preferably in a concentration of from 80 to120%, more preferably from 85 to 105%, most preferably from 88 to 99%.For the sulfuric acid, in the present invention, concentration figuresmore than 100% mean solutions of sulfur trioxide (SO₃) in 100% sulfuricacid. For instance, a sulfuric acid concentration of 120% is understoodto mean a 20% solution of SO₃ in 100% sulfuric acid.

It is advantageous to establish the necessary acid concentration bymixing sulfuric acid of a relatively high concentration and of arelatively low concentration, in which case the sulfuric acid with arelatively low concentration used may be recovered sulfuric acid fromearlier sulfonation reactions. The mixing of the sulfuric acid can beeffected in the sulfonation reactor in the presence of the bead polymerto be sulfonated, such that the resulting heat of mixing leads to atemperature increase in the reaction mixture.

The ratio of sulfuric acid to bead polymer is from 2.0 to 6 ml/g,preferably from 2.5 to 5 ml/g, more preferably from 2.6 to 4.2 ml/g.

If desired, a swelling agent, preferably chlorobenzene, dichloroethane,dichloropropane or methylene chloride, can be employed in thesulfonation. The swelling agent is used preferably in amounts of from0.1 to 1 ml per gram of dry bead polymer, more preferably from 0.2 to0.5 ml per gram of dry bead polymer. The swelling agent is preferablyadded to the bead polymer initially charged in sulfuric acid before theonset of the sulfonation reaction.

The temperature in the sulfonation is generally 50-200° C., preferably80-160° C., more preferably 90-140° C. It may be advantageous to employa temperature program in the sulfonation, in which the sulfonation iscommenced at a first temperature in a first reaction step and continuedat a higher temperature in a second reaction step.

In the sulfonation, the reaction mixture is stirred. It is possible touse different stirrer types, such as paddle stirrers, anchor stirrers,gate stirrers or turbine stirrers.

The duration of the sulfonation reaction is generally several hours,preferably between 1 and 24 h, more preferably between 2 and 16 h, mostpreferably between 3 and 12 h.

After the sulfonation, the reaction mixture composed of sulfonationproduct and residual acid is cooled to room temperature and dilutedfirst with sulfuric acids of decreasing concentrations and then withwater.

If desired, the cation exchanger obtained in accordance with theinvention can be treated in the H form, for purification, with deionizedwater at temperatures of 70-180° C., preferably of 105-130° C.

For many applications, it is favorable to convert the cationic exchangerfrom the acidic form to the sodium form. This conversion is effectedwith sodium hydroxide solution of a concentration of 2-60% by weight,preferably 4-10% by weight, or with aqueous sodium chloride solutionswhich are 1-25% by weight, preferably 4-10% by weight, in sodiumchloride.

After the conversion, the cation exchangers can be purified further bytreating with deionized water or aqueous salt solutions, for examplewith sodium chloride or sodium sulfate solutions. It has been found thatthe treatment at 70-150° C., preferably 120-135° C., is particularlyeffective and does not bring about any reduction in the capacity of thecation exchanger.

The inventive, strongly acidic cation exchangers may contain pores.Porous inventive strongly acidic cation exchangers may be microporous,mesoporous and/or macroporous. For the definition of the terms“gel-form”, “porous”, “microporous”, “mesoporous” and “macroporous” forpolymers, reference is made to Pure Appl. Chem., Vol. 76, No. 4, p.889-906, 2004 (IUPAC recommendations 2003), more particularly to p. 900§3.9 and p. 902-903 §3.23.

The inventive, strongly acidic cation exchangers have a mean particlesize D between 30 μm and 1000 μm, preferably between 100 and 800 μm. Todetermine the mean particle size and the particle size distribution,customary methods, such as screen analysis or image analysis, aresuitable. The mean particle size D is understood in the context of thepresent invention to mean 50% value (Ø (50)) of the volume distribution.The 50% value (Ø (50)) of the volume distribution indicates the diameterwhich is above that of 50% by volume of the particles.

In a preferred embodiment of the present invention, monodispersestrongly acidic cation exchangers are produced. Monodisperse particlesize distributions in the context of the present invention have aproportion by volume of particles between 0.9 D and 1.1 D of at least75% by volume, preferably at least 85% by volume, more preferably atleast 90% by volume.

The present invention also relates to a process for producing stronglyacidic cation exchangers, characterized in that:

-   -   a) monodisperse or heterodisperse bead polymers are prepared        from vinylaromatic monomers, crosslinkers and from 0.2 to 20% by        weight of vinyl ethers and/or vinyl esters by suspension        polymerization and    -   a) these bead polymers are converted to strongly acidic cation        exchangers by the action of sulfuric acid, sulfur trioxide        and/or chlorosulfonic acid.

The strongly acidic cation exchangers obtained by the process accordingto the invention are notable for a particularly high mechanicalstability, osmotic stability and oxidation stability. Even afterprolonged use and multiple regeneration, they exhibit barely any defectsin the ion exchanger spheres.

For the inventive strongly acidic cation exchangers, there is amultitude of different applications. For example, they can be used indrinking water treatment, in the production of power plant water andultrapure water (needed in microchip production for the computerindustry), for chromatographic separation of glucose and fructose and ascatalysts for various chemical reactions (for example bisphenol Apreparation from phenol and acetone).

It will be understood that the specification and examples areillustrative but not limitative of the present invention and that otherembodiments within the spirit and scope of the invention will suggestthemselves to those skilled in the art.

Analysis Methods:

Volume-Based Total Capacity

20 ml of exchanger are shaken in under demineralized water on a tampingvolumeter. In a 200 ml beaker, these 20 ml of exchanger, 5 g of NaClp.a. and 50 ml of sodium hydroxide solution c(NaOH)=1 mol/l are combinedand titrated with hydrochloric acid c(HCl)=1.0 mol/l down to pH=4.3.

The total capacity of the cation exchanger is calculated as follows:

${TC} = \frac{{{Consumption}\mspace{14mu} {of}\mspace{14mu} {HCl}\mspace{14mu} {c({HCl})}} = {1.0\mspace{14mu} {{mol}/l}}}{20}$

Original Stability: Number of Perfect Beads After Production

100 beads are viewed under a microscope. The number of beads which bearcracks or exhibit splintering-off is determined. The number of perfectbeads is calculated from the difference between the number of damagedbeads and 100.

Determination of the Osmotic Stability of Cation Exchangers ThroughSwelling Stability

In the swelling stability test, the exchangers are treated in a filtertube alternately with hydrochloric acid w(HCl)=6% and sodium hydroxidesolution w(NaOH)=4%. There is intermediate treatment in each case withdemineralized water.

For the test, 25 ml of exchanger shaken in under demineralized water areinstalled into a filter tube.

Then the resin is rinsed back with demineralized water for 5 minutes.The rate of back-rinsing is regulated such that the resin is distributedover the entire filter tube length.

After the back-rinsing has ended, 40 working operations are carried out.One working operation comprises 4 cycles of 10 minutes each of loadingand regeneration and 2×5 minutes each of back-rinsing. Acid and alkalirun through the exchangers at 500 ml per cycle through capillaries.

After the test has ended, the exchanger is flushed out of the filtertube, and the water is sucked in with the screen tube and mixedthoroughly.

The exchanger is then counted under the microscope for the percentage ofwhole beads, of cracked beads and splinters as in the determination ofthe original stability.

Determination of the Oxidation Stability of Cation Exchangers byReddening Test

750 ml of resin are shaken in and washed in cocurrent with UPW water ata rate of 15 l/h for 4 hours. UPW water is defined as water having aconductivity of <17.8 MOhm cm and a content of organic material (TOC)<2.00 ppb. After the washing, the 750 ml of resin are subjected tosuction on a glass suction filter for 5 minutes. For the conductivity ofUPW, see also 1998 Semiconductor Pure Water and Chemicals Conference,Mar. 2-5, 1998, Advances in Resistivity Instrumentation for UPW Systemsof the Future, Anthony C. Bevilacqua under:

http://www.gatewayequipment.com/whitepapers/resistivity_instru_futureUPWsystems.pdf.

50 g of the washed and suctioned cation exchanger are transferred into aglass bottle. The closed glass bottle is stored in daylight at roomtemperature for 4 weeks. At the end of the storage time, the resin isadmixed with 100 g of UPW water and shaken at 100 rpm for 10 minutes.Subsequently, the sample is filtered off and the eluate is tested by thefollowing methods: pH, absorbance at 225 nm (1 cm cuvette) and visualassessment of reddening, the mark 0 indicating a completely colorlesseluate and the mark 4 a deep red eluate.

Demineralized water in the context of the present invention ischaracterized in that it possesses a conductivity of from 0.1 to 10 μS,the content of dissolved or undissolved metal ions being not greaterthan 1 ppm, preferably not greater than 0.5 ppm for Fe, Co, Ni, Mo, Cr,Cu as individual components, and being not greater than 10 ppm,preferably not greater than 1 ppm, for the total of the metalsmentioned.

EXAMPLES Example 1 Preparation of a Monodisperse Seed Bead Polymer Basedon styrene, divinylbenzene and ethylstyrene

A 4 l glass reactor was initially charged with 1020 g of demineralizedwater, and a solution of 3.2 g of gelatin, 4.8 g of disodiumhydrogenphosphate dodecahydrate and 0.24 g of resorcinol in 86 g ofdemineralized water was added and mixed. The temperature of the mixturewas adjusted to 25° C. With stirring, 1182 g of microencapsulatedmonomer droplets which had been obtained by jetting and had a narrowparticle size distribution, containing 4.5% by weight of divinylbenzene,1.12% by weight of ethylstyrene, 0.36% by weight of tert-butylperoxy-2-ethylhexanoate and 94.02% by weight of styrene, were added withstirring, the microcapsules having consisted of a formaldehyde-hardenedcomplex coacervate of gelatin and a copolymer of acrylamide and acrylicacid, and 1182 g of aqueous phase with a pH of 12 were added.

The mixture was polymerized to completion with stirring by increasingthe temperature according to a temperature program beginning at 25° C.and ending at 95° C. The mixture was cooled, washed over a 315 μm screenand then dried at 80° C. under reduced pressure. 1152 g of a seed beadpolymer having a mean particle size of 365 μm, and narrow particle sizedistribution and a smooth surface were obtained.

Comparative Example 1 (Noninventive) CIa) Preparation of a Bead Polymerwithout Comonomer

In a 4 l stirred reactor with gate stirrer, cooler, temperature sensorand thermostat and temperature recorder, an aqueous initial chargecomposed of 1443 g of deionized water and 5.88 g of disodiumhydrogenphosphate dodecahydrate was obtained. To this initial chargewere added, with stirring at 200 rpm, 864.9 g of seed polymer fromexample 1.

Within 30 min, a mixture of 625.7 g of styrene, 109.5 g ofdivinylbenzene (81.3%) and 5.88 g of dibenzoyl peroxide was added. Toremove atmospheric oxygen, the mixture was then sparged with nitrogenfor 15 minutes. Subsequently, the reactor contents were brought to 30°C. within 30 minutes and kept at this temperature for a further 30minutes. Then a solution of 3.2 g of methylhydroxyethylcellulosedissolved in 157 g of water was added and the mixture was stirred at 30°C. for another hour. The mixture was heated to 62° C. for 16 hours andthen to 95° C. for 2 hours. After cooling, the mixture was washed over a315 μm screen and dried. 1465 g of a monodisperse bead polymer having amean particle size of 448 μm were obtained.

C1b) Production of a Cation Exchanger

A 4 l stirred reactor with gate stirrer, temperature sensor,distillation system and thermostat and temperature recorder wasinitially charged with 741 ml of 87.8% by weight sulfuric acid at roomtemperature. Within 30 minutes, 350 g of bead polymer from C1a) and 88ml of 1,2-dichloroethane were introduced with stirring. The reactorcontents were stirred at 40° C. for 30 minutes. Subsequently, 159 ml ofoleum (65% by weight SO₃ in 100% by weight sulfuric acid) were addedwithin one hour without the reactor temperature exceeding 90° C. Thenthe mixture was heated to 115° C. and stirred at 115° C. for 5 hours, inthe course of which the 1,2-dichloroethane was removed by means of adistillation system. The reaction mixture was subsequently brought to140° C. and stirred at 140° C. for 3 hours. After cooling, thesuspension was transferred to a glass column. Sulfuric acid ofdecreasing concentration, beginning with 90% by weight and ending withpure water, was applied to the column from the top. 1460 ml ofmonodisperse cation exchanger in the H form with a total capacity, basedon the H form, of 2.08 eq/l were obtained.

Comparative Example 2 (Noninventive) C2a) Preparation of a Bead Polymerwithout Comonomer

In a 4 I stirred reactor with gate stirrer, condenser, temperaturesensor and thermostat and temperature recorder, an aqueous initialcharge composed of 1342 g of deionized water, 5.3 g of boric acid and2.97 g of 50% by weight sodium hydroxide solution was obtained. To thisinitial charge were added, with stirring at 200 rpm, 802.4 g of seedpolymer prepared according to example 1.

Within 30 min. a mixture of 687.7 g of styrene, 114.7 g ofdivinylbenzene (80.5%) and 2.57 g of tert-butyl peroxy-2-ethylhexanoatewas added. To remove atmospheric oxygen, the mixture was then spargedwith nitrogen for 15 minutes. Subsequently, the reactor contents werebrought to 30° C. within 30 minutes and kept at this temperature for afurther 2 hours. A solution of 3.2 g of methylhydroxyethylcellulosedissolved in 157 g of water was then added and the mixture was stirredat 30° C. for another hour. The mixture was heated to 65° C. for 11hours and then to 95° C. for 2 hours. After cooling, the mixture waswashed over a 315 μm screen and dried. 1544 g of a monodisperse beadpolymer having a mean particle size of 460 μm were obtained.

C2b) Production of a Cation Exchanger

A 4 l stirred reactor with gate stirrer, temperature sensor,distillation system and thermostat and temperature recorder wasinitially charged with 1400 ml of 98% by weight sulfuric acid and heatedto 100° C. Within 30 minutes, 350 g of bead polymer from C2a) wereintroduced in 10 portions with stirring. Subsequently, the mixture wasstirred at 100° C. for 30 minutes and at 115° C. for 5 hours. Aftercooling, the suspension was transferred into a glass column. Sulfuricacid of decreasing concentration, beginning with 90% by weight andending with pure water, was applied to the column from the top.

1440 ml of monodisperse cation exchanger in the H form with a totalcapacity, based on the H form, of 2.2 eq/l were obtained.

Comparative Example 3 (Noninventive) C3a) Preparation of a Bead Polymerwith Acrylonitrile According to DE-A 10 122 896

The procedure was as in example C2a), except that 4.71 g of boric acidand 2.64 g of 50% by weight sodium hydroxide solution were used in theinitial charge. To this were added 891.5 g of seed polymer, prepared asin example 1, and a mixture of 560.3 g of styrene, 88.7 g ofdivinylbenzene (81.3%), 64.2 g of acrylonitrile and 2.28 g of tert-butylperoxy-2-ethylhexanoate. The mixture was heated to 61° C. for 11 hoursand then to 130° C. for 2 hours.

1505 g of a monodisperse bead polymer having a mean particle size of 442μm were obtained.

C3b) Production of a Cation Exchanger

The procedure was as in example C2b), except that 2800 ml of 98% byweight sulfuric acid were initially charged and 700 g of bead polymerfrom C3a) were introduced and the mixture was stirred at 105° C. for 5hours.

3000 ml of monodisperse cationic exchanger in the H form with a totalcapacity, based on the H form, of 1.92 eq/l were obtained.

Example 2 (Inventive) 2a) Preparation of a Bead Polymer with diethyleneglycol divinyl ether

In a 4 l stirred reactor with gate stirrer, condenser, temperaturesensor and thermostat and temperature recorder, an aqueous initialcharge composed of 1443 g of deionized water and 5.88 g of disodiumhydrogenphosphate dodecahydrate was obtained. To this initial chargewere added, with stirring at 200 rpm, 864.9 g of seed polymer preparedas in example 1.

Within 30 min, a mixture of 625.7 g of styrene, 109.5 g ofdivinylbenzene (81.4%) and 5.88 g of dibenzoyl peroxide was added. Toremove atmospheric oxygen, the mixture was then sparged with nitrogenfor 15 minutes. Subsequently, the reactor contents were brought to 30°C. within 30 minutes and kept at this temperature for 30 minutes. Asolution of 3.2 g of methylhydroxyethylcellulose dissolved in 157 g ofwater was then added, and the mixture was stirred at 30° C. for another1 hour. The mixture was heated to 62° C. for 16 hours. Then 30 g ofdiethylene glycol divinyl ether and a solution of 5 g of potassiumperoxodisulfate in 50 ml of water were added at 62° C. in two separatefeeds within 30 minutes. The mixture was then heated to 95° C. for 2hours. After cooling, the mixture was washed over a 315 μm screen anddried. 1539 g of a monodisperse bead polymer having a mean particle sizeof 448 μm were obtained.

2b) Production of a Cation Exchanger

The procedure was as in example C3b), except that 700 g of bead polymerfrom 2a) were introduced and the mixture was stirred at 115° C. for 10hours instead of at 105° C. for 5 hours.

3920 ml of monodisperse cation exchanger in the H form with a totalcapacity, based on the H form, of 2.12 eq/l were obtained.

Example 3 (Inventive) 3a) Preparation of Bead Polymers with diethyleneglycol divinyl ether

In a 4 l stirred reactor with gate stirrer, condenser, temperaturesensor and thermostat and temperature recorder, an aqueous initialcharge composed of 1443 g of deionized water, 4.85 g of boric acid and2.72 g of 50% by weight sodium hydroxide solution was obtained. To thisinitial charge were added, with stirring at 200 rpm, 864.9 g of seedpolymer prepared as in example 1.

Within 30 min, a mixture of S g of styrene (see table), 109.5 g ofdivinylbenzene (81.3%), X g of diethylene glycol divinyl ether (DEGDVE,see table) and 2.35 g of tert-butyl peroxy-2-ethylhexanoate was added.To remove atmospheric oxygen, the mixture was then sparged with nitrogenfor 15 minutes. Subsequently, the reactor contents were brought to 30°C. within 30 minutes and kept at this temperature for 30 minutes. Then asolution of 3.2 g of methylhydroxyethylcellulose dissolved in 157 g ofwater was added and the mixture was stirred at 30° C. for another hour.The mixture was heated to 65° C. for 11 hours and then to 95° C. for 2hours. After cooling, the mixture was washed over a 315 μm screen anddried. Y g of a monodisperse bead polymer were obtained (see table).

3b) Production of Cation Exchangers

The procedure was as in example C2b), except that in each case 350 g ofbead polymer from 3a) were introduced.

Z ml of monodisperse cation exchanger in the H form with a totalcapacity, based on the H form, of TC eq/l were obtained (see Tab. 1).

TABLE 1 Amount S Amount X of Yield Y of Yield Z of TC of the Example ofstyrene DEGDVE polymer resin resin 3.1 618.3 g  7.4 g 1575 g 1400 ml2.20 eq/l 3.2 603.5 g 22.2 g 1574 g 1400 ml 2.18 eq/l 3.3 588.7 g 37.0 g1580 g 1380 ml 2.17 eq/l

Example 4 (Inventive) 4a) Preparation of a Bead Polymer with butanedioldivinyl ether

The procedure was as in example 2a), except that 30 g of butanedioldivinyl ether were used instead of 30 g of ethylene glycol divinylether.

1550 g of a monodisperse bead polymer were obtained.

4b) Production of a Cation Exchanger

A 4 l stirred reactor with gate stirrer, temperature sensor,distillation system and thermostat and temperature recorder wasinitially charged with 1200 ml of 98% by weight sulfuric acid and heatedto 100° C. Within 30 minutes, 300 g of bead polymer from 4a) wereintroduced in 10 portions with stirring. Subsequently, the mixture wasstirred at 115° C. for 5 hours and at 135° C. for 2 hours. Aftercooling, the suspension was transferred into a glass column. Sulfuricacid of decreasing concentration, beginning with 90% by weight andending with pure water, was applied to the column from the top.

1280 ml of monodisperse cation exchanger in the H form with a totalcapacity, based on the H form, of 2.19 eq/l were obtained.

Example 5 (Inventive) 5a) Preparation of a Bead Polymer with ethyleneglycol monovinyl ether

The procedure was as in example 2a), except using 30 g of ethyleneglycol monovinyl ether instead of 30 g of ethylene glycol divinyl ether.

1670 g of a monodisperse bead polymer were obtained.

5b) Production of a Cation Exchanger

The procedure was as in example 4b), except that 1400 ml of 98% byweight sulfuric acid were initially charged and 350 g of bead polymerfrom 5a) were introduced.

1470 ml of monodisperse cation exchanger in the H form with a totalcapacity, based on the H form, of 2.21 eq/l were obtained.

Example 6 (Inventive) 6a) Preparation of a Bead Polymer with vinylacetate

The procedure was as in example 2a), except that 30 g of vinyl acetatewere used instead of 30 g of ethylene glycol divinyl ether.

1264 g of a monodisperse bead polymer were obtained.

6b) Production of a Cation Exchanger

The procedure was as in example 5b with 350 g of bead polymer from 6a).

1480 ml of monodisperse cation exchanger in the H form with a totalcapacity, based on the H form, of 2.17 eq/l were obtained.

Example 7 (Inventive) 7a) Preparation of a Bead Polymer with diethyleneglycol divinyl ether

Example 2a was repeated. 1570 g of a monodisperse bead polymer wereobtained.

7b) Production of a Cation Exchanger

The procedure was analogous to comparative example C1b), except that 664ml of 84.7% by weight sulfuric acid were initially charged at roomtemperature and 350 g of bead polymer from 7a) were used and 227 ml ofoleum were added.

1500 ml of monodisperse cation exchanger in the H form with a totalcapacity, based on the H form, of 2.08 eq/l were obtained.

Example 8 (Inventive) 8a) Preparation of a Bead Polymer with diethyleneglycol divinyl ether

In a 4 l stirred reactor with gate stirrer, condenser, temperaturesensor and thermostat and temperature recorder, an aqueous initialcharge composed of 1400 g of deionized water, an aqueous initial chargecomposed of 1400 g of deionized water, 6.88 g of disodiumhydrogenphosphate dodecahydrate and 90.3 g of a 2% aqueous solution ofmethylhydroxyethylcellulose was obtained.

Thereafter, a mixture of 1316.4 g of styrene, 137.7 g of divinylbenzene(80.3%), 14.7 g of diethylene glycol divinyl ether and 11.8 g ofdibenzoyl peroxide (75% by weight in water) was added. The reactorcontents were left to stand at room temperature for 30 minutes, in thecourse of which two phases formed. Then the stirrer was switched on at180 rpm and the mixture was stirred at room temperature for 30 minutes.The reactor contents were subsequently heated at 62° C. for 16 hours andat 95° C. for 2 hours. After cooling, the mixture was washed over a 315μm screen and dried. 1441 g of a heterodisperse bead polymer wereobtained.

8b) Production of a Cation Exchanger

The procedure was analogous to comparative example C1b), except that1110 ml of 86% by weight sulfuric acid were initially charged at roomtemperature, 350 g of bead polymer from 8a) were used and 322 ml ofoleum were added. The mixture was stirred only at 115° C. for 5 hours(without the 140° C. stage).

1590 ml of heterodisperse cation exchanger in the H form with a totalcapacity, based on the H form, of 1.90 eq/l were obtained.

Example 9 (Inventive) 9a) Preparation of a Macroporous Bead Polymer withdiethylene glycol divinyl ether

In a 4 l stirred reactor with gate stirrer, condenser, temperaturesensor and thermostat and temperature recorder, an aqueous initialcharge composed of 1112 g of deionized water, 7.86 g of disodiumhydrogenphosphate dodecahydrate and 149 g of a 2.2% aqueous solution ofmethylhydroxyethylcellulose was obtained.

Thereafter, a mixture of 812 g of styrene, 140.2 g of divinylbenzene(81.8%), 19.1 g of diethylene glycol divinyl ether, 421 g of isododecaneand 5.73 g of tert-butyl peroxy-2-ethylhexanoate was added. The reactorcontents were left to stand at room temperature for 20 minutes, in thecourse of which two phases formed. Then the stirrer was switched on at300 rpm and the mixture was stirred at room temperature for 30 minutes.The reactor contents were then stirred at 70° C. for 7 hours and at 95°C. for 2 hours. After cooling, the mixture was washed over a 315 μmscreen and dried. 959 g of a macroporous, heterodisperse bead polymerwere obtained (r=revolutions).

9b) Production of a Macroporous Cation Exchanger

The procedure was analogous to comparative example C2b), except that 350g of bead polymer from 9a) were introduced into the sulfuric acid at115° C. (instead of at 100° C.).

1600 ml of heterodisperse cation exchanger in the H form with a totalcapacity, based on the H form, of 1.90 eq/l were obtained.

Comparative Example 4 (Noninventive) C4a) Preparation of a MacroporousBead Polymer without Comonomer

The procedure was as in example 9a), except that the diethylene glycoldivinyl ether was omitted. 936 g of a macroporous, heterodisperse beadpolymer were obtained.

C4b) Production of a Macroporous Cation Exchanger

The procedure was as in example 9b), except that 350 g of bead polymerfrom C4a) were introduced into the sulfuric acid at 115° C.

1640 ml of heterodisperse cation exchanger in the H form with a totalcapacity, based on the H form, of 1.87 eq/l were obtained.

TABLE 2 Test results for osmotic and oxidation stability of examples 2to 9 and of comparative examples 1 to 4 Reddening test after 4 weeksExample TC (eq/l) OS SS pH Abs. 225 nm Mark C1 2.08 90 84 3.33 2.91 1 C22.20 97 n.d. 3.38 2.10 2 C3 1.92 97 89 2.79 >4 3 C4 1.87 100 n.d. 3.462.57 2 2 2.12 95 93 3.64 0.59 1 3.1 2.20 94 92 3.55 1.19 1 3.2 2.18 9891 3.50 0.95 1 3.3 2.17 96 95 3.62 0.61 0 4 2.19 97 97 3.57 0.61 1 52.21 99 96 3.54 1.22 1 6 2.17 98 90 3.54 1.04 2 7 2.08 99 85 3.58 0.70 18 1.90 95 n.d. 3.56 2.00 2 9 1.90 100 n.d. 3.61 1.64 3 TC = totalcapacity; OS = original stability; SS = swelling stability

Example 10 Determination of the Oxidation Stability of the Resins

The resins from examples 2 to 8 and from comparative examples C1 to C3were subjected to the reddening test.

The pH gives information as to how much soluble acid (principallypolystyrenesulfonic acid, so-called leaching, combined with smallamounts of sulfuric acid from the hydrolysis of the sulfonic acid groupsof the resin) has been formed under air after a given storage time; theabsorption at 225 nm is a measure for the water-soluble aromaticcompounds released, in this case oligomeric and polymericstyrenesulfonic acids.

In the test:

the higher the pH of the eluate, the smaller the amount of soluble acidwhich has been released by the resin, and the higher the oxidationstability of the resins;

the lower the absorption value of the eluate at 225 nm, the smaller theamount of soluble aromatic compounds which has been released by theresin, and the higher the oxidation stability of the resins;

the lower the mark in the visual assessment of the eluate, the morecolorless the eluate.

The results of the osmotic stability and of the oxidation stability testfor the different examples and comparative examples are reported in Tab.2.

Tab. 2 shows that the inventive strongly acidic cation exchangerspossess total capacities which are in no way inferior to the totalcapacity of the comparative examples.

It can be seen that the inventive strongly acidic cation exchangers havevery high original and swelling stability values which are comparable toor higher than the values of the comparative examples corresponding tothe state of the art.

All inventive cationic exchangers have, in the reddening test, a higherpH of the eluate and a lower absorption value of the eluate at 225 nmthan the comparative examples. This demonstrates a significantly reducedrelease of soluble polystyrenesulfonic acids from the inventive resinsand hence the higher oxidation stability of the inventive resins.

Tab. 2 also shows that the improvement in the profile of properties ofthe inventive strongly acidic cation exchangers is particularly markedfor the divinyl ether compounds (examples 2, 3, 4, 7).

Comparison of examples 2, 3 and 4 shows that the effect of adding vinylether and/or vinyl ester in the polymerization is independent of thetype and of the time of comonomer incorporation.

Example 9 compared with comparative example 4 reveals that theimprovement in the oxidation stability of the strongly acidic cationexchangers as a result of the inventive incorporation of vinyl ether(s)and/or vinyl ester(s) also occurs in the case of macroporous resins.

1. Strongly acidic cation exchangers obtained by sulfonating bead polymers formed from vinylaromatic monomers, crosslinkers and from 0.2 to 20% by weight of vinyl ethers and/or vinyl esters.
 2. Strongly acidic cation exchangers according to claim 1, wherein the bead polymers are copolymers of at least one monoethylenically unsaturated, aromatic monomer, at least one crosslinker and at least one vinyl ether or vinyl ester.
 3. Strongly acidic cation exchangers as claimed in claim 1 having a monodisperse particle size distribution.
 4. Strongly acidic cation exchangers as claimed in one of claim 1 obtained from bead polymers having been prepared by the seed-feed process.
 5. A process for producing strongly acidic cation exchangers, wherein: a) monodisperse or heterodisperse bead polymers are prepared from vinylaromatic monomers, crosslinkers and from 0.2 to 20% by weight of vinyl ethers and/or vinyl esters by suspension polymerization and b) these bead polymers are converted to strongly acidic cation exchangers by the action of sulfuric acid, sulfur trioxide and/or chlorosulfonic acid.
 6. A method of using of the strongly acidic cation exchangers according to claim 1 in drinking water treatment, in the production of power water and ultrapure water, for chromatographic separation of glucose and fructose, and as catalysts for various chemical reactions.
 7. A method of using as claimed in claim 6, wherein the strongly acidic cation exchangers are used as catalysts in the bisphenol A preparation from phenol and acetone.
 8. Strongly acidic cation exchangers as claimed in claim 1 having a microporous particle size distribution. 